Prostaglandins increase GTP hydrolysis by membranes from human mononuclear cells

Both adenylate cyclase and GTPase activities in human mononuclear cell membranes were increased by prostaglandins. Adenylate cyclase activity, however, was enhanced by much lower concentrations of PGE1 (prostaglandin E1) than were required to increase GTPase. PGE2, PGA1, PGB1, and PGF1 alpha also stimulated GTPase activity. These same prostaglandins, with the notable exception of PGF1 alpha, increased adenylate cyclase activity (PGE2 greater than PGA1 greater than or equal to PGB1). Isoproterenol, 100 microM, doubled adenylate cyclase without altering GTPase activity. Choleragen activated adenylate cyclase in mononuclear cell membranes but had no effect on GTPase activity whether or not PGE1 was present. Mononuclear cells were separated into adherent and nonadherent populations by two different methods to examine the possibility that the prostaglandin-stimulated GTPase was confined to a specific type of mononuclear cell. Adenylate cyclase in membranes from both adherent and nonadherent cells was activated by PGE1, but neither PGE1 nor choleragen altered GTPase activity in these preparations. It appears that, although several prostaglandins can increase GTPase activity in mononuclear cell membranes, the increase in GTPase activity is not consistently associated with activation of adenylate cyclase by prostaglandins.